B-doped Be coatings for NIF target development

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2007-07, Vol.25 (4), p.1203-1207
• Main Authors: Xu, H., Moreno, K. A., Youngblood, K. P., Nikroo, A., Hackenberg, R. E., Cooley, J. C., Alford, C. S., Letts, S. A.
• Format: Article
• Language: English
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.2747622

Sputtered beryllium and copper-doped beryllium coatings as thick as 170 μ m have been deposited on spherical substrates to produce hollow shells that are required as targets for inertial fusion experiments. Be coatings by magnetron sputtering achieved ∼ 95 ± 2 % bulk density consistently up to 170 μ m thick. Coatings on the spherical substrates exhibit the typical columnar structure throughout the entire thickness. Transmission electron microscopy indicates the presence of submicron, nearly spherical voids mainly aggregated along the columnar structure and grain boundaries, as well as some smaller intragranular elongated voids. Holes have been drilled in beryllium shells produced in this manner to allow filling with deuterium (the fusion fuel). Gas retention of these shells has been examined using mass spectrometry. It appears that a fraction of the pores in the coatings are interconnected, which leads to leakage of the hollow shells. Boron-doped Be layers near the eutectic phase, at a concentration of ∼ 11 at. % , have been added to the Be shells to significantly improve D 2 gas retention of the shells. However, there remains a considerable scatter in the measured leakage.